The invention relates to devices for attenuating noise generated by rolling tire and wheel assemblies of the type defining a closed interior cavity, for example, pneumatic tire and wheel assemblies. More particularly, the invention relates to a device mounted in a tire cavity for attenuating noise relating to cavity vibration modes.
Cavity noise in tires is generated by the excitation of the air contained inside the closed tire cavity. Generally, the air is excited by the deflection of the tire tread and sidewalls when the tire is rolling. The air in the cavity, although confined in a toroidal cavity, acts as an air column under the effect of the excitation. Various solutions have been proposed to reduce or eliminate cavity noise, including Helmholtz resonators incorporated in the wheel and sound absorbing materials arranged in various configurations in the cavity. These solutions themselves have difficulties including high cost, manufacturability, and effectiveness.
The present invention proposes a solution for reducing cavity noise that is simple, inexpensive, easy to manufacture, and effective.
The invention starts from the point that a closed cavity defined by a tire mounted on a wheel defines a toroidal space which is substantially uniform in the circumferential direction. During rotation of the tire, the substantially uniform space acts as an infinitely long tube of air and allows standing acoustic waves to form in the cavity. The energy of the waves is transmitted through the wheel to the vehicle as noise. The inventor realized that while the acoustic wave can be thought of as a standing wave in the cavity, the rotating tire and wheel could be thought of as moving relative to the wave. Thus, by placing a device on the tire or wheel to interfere with the maximum and minimum peaks of a wave, the wave could be attenuated.
According to the invention, acoustic waves can be disturbed and the transmission of energy to the wheel attenuated by a device that provides non-uniformities in the cavity circumferential direction. Such a device, according to the invention, comprises at least one circumferential ring providing a non-continuous profile of alternating ridges and gaps. The at least one ring is located in the tire cavity on a surface of the tire or the wheel.
According to one embodiment, the ring is formed from a plurality of strips in circumferential alignment and mutually spaced to have one or more gaps. According to another embodiment, the ring is formed of a single strip having a plurality of ridges separated by gaps formed in the strip. It is believed that the profile of raised and lower surfaces (strips/ridges and gaps) moves through the acoustic wave so that ridge momentarily coincides with the wave peak, causing an interruption, and thus diminishing the noise generated by the tire cavity.
The number of the ridges and gaps is related to the order of the acoustic wave to be attenuated by the device. As will be understood by those skilled in the art, the first-order mode is a complete wave occurring once per revolution, meaning the wave will have two peaks, at a maximum and a minimum about the circumference of the tire. A ring in accordance with the invention for attenuating a first order mode vibration provides at least two equally spaced ridges and gaps. Preferably, the ring comprises four ridges and gaps, which is believed to facilitate the interrupting capability of the ring.
According to the invention, the alternating position of the ridges and gaps provides the improved waved interrupting function as compared to a continuous ring of absorbent material, as known in the art. The ridges and gaps can be of equal circumferential length. Alternatively, the ridges can be longer than the gaps, or the gaps longer than the ridges, the ridges being substantially of equal length, and the gaps being substantially of equal length.
According to a preferred embodiment of the invention, the ring is formed of sound absorbing material to assist noise reduction by absorbing some of the sound energy and not providing sound reflective surfaces.
According to an aspect of the invention, wave interruption can be improved by placing two rings in the tire cavity in parallel and mutually oriented so that the gaps in each ring are positioned relatively staggered about the circumference so as not to be aligned in the lateral or axial direction.
The rings may be positioned on the cavity-defining surfaces of the tire or the wheel or both. Preferably, the rings are located on the crown of the tire or the well region of the wheel between the bead seats so that mounting or dismounting the tire does not damage the strips.
The strips forming the rings are formed of a material capable of being mounted in the tire and withstanding the tire environment and stresses from rolling and other deflections. Rubber or plastic strips, metallic, textile, or composite materials can be placed in the tire cavity, understanding that non-flexible or rigid materials are more suitable for placement on the wheel rather than the tire.
The sound absorbing strips may be formed of any material capable of absorbing acoustic or vibration energy, for example, rubber, foamed rubber and plastic, cork, textiles, or felts.